1. Technological Field
The present invention relates to a blood pressure measurement device and blood pressure measurement method.
2. Background Technology
Medical insurance in Japan applied insurance points to 24-hour blood pressure gauges for the first time due to a change to insurance medical fee points in 2008. This came about as a result of medical and administrative recognition that a correct diagnosis of high blood pressure cannot be made based on a single blood pressure measurement from a specific time. Such a recognition is a breakthrough in understanding high blood pressure, and indicates a need for a new generation in blood pressure management that goes beyond conventional blood pressure management.
Specifically, blood pressure values vary continually, and by precisely comprehending this variation to achieve a level of blood pressure management not heretofore possible by the conventional technique, it may become possible to reduce the current incidence of circulatory system diseases, increase the QOL of individuals in the future aging society, bring down total health care cost for the entire country, and avert medical financial bankruptcy.
The two methods described below are now commonly used for noninvasive measurement of blood pressure. The first method is known as auscultation. After applying a pressure equal to or greater than the systolic blood pressure value from outside an artery, the pressure is gradually relieved, whereupon the blood vessel audibly pulsates in a specific pressure range and emits a so-called Korotkoff sound. Auscultation is a method in which the pressure value when the Korotkoff sound begins to occur at the abovementioned relieving of pressure is determined as the systolic blood pressure, and the pressure value when the sound disappears is determined as the diastolic blood pressure.
The second method is known as the oscillometric method. When pressure is applied from the outside in the same manner as in the auscultation method, since the mechanical characteristics of the arterial wall are nonlinear, the volume of the blood vessel varies with each heartbeat, and the pulse wave amplitude varies in nonlinear fashion. After a pressure equal to or greater than the systolic blood pressure is applied in the same manner as in the auscultation method, the pressure is gradually relieved, whereupon the blood vessel begins to pulsate when the pressure applied is below the systolic blood pressure, and after the maximum volume variation occurs at the average blood pressure, the pulse wave pulsation again disappears at or below the diastolic blood pressure. By thus simultaneously recording the pressure value as well as the volume variation of the blood vessel at the time the pressure value occurs, the systolic blood pressure, the average blood pressure, and the diastolic blood pressure can be determined. The oscillometric method is widely used by particularly in blood pressure gauges worn on the wrist, since a pulse waveform is relatively easy to express as an electrical signal.
The medical definition of blood pressure is the intravascular pressure in the aortic root, and another blood pressure value measured noninvasively is thus an estimate of the true blood pressure. Since blood also naturally has weight, measurement of blood pressure by the auscultation method or the oscillometric method must take place at the same height as the heart. In a common blood pressure gauge, in the case of measurement at the upper arm, for example, the cuff must be worn at the same height as the heart, and for measurement at the wrist, the wrist must be raised to the height of the heart. Otherwise, a correction must be made in accordance with the difference in height with respect to the heart (so-called water head correction). Since the correction for height corresponds to 10 mmHg for a water head of 13.6 cm, for example, a correction of approximately 7.35 mmHg must be made for every 10 cm.
A blood pressure measurement device has been disclosed in which angle detection means is provided for the upper arm in addition to a forearm angle detection means, and the height of a cuff and the heart are detected based on the detected angles of the forearm and upper arm (see Patent Document 1, for example).
In another blood pressure measurement device (see Patent Document 2, for example), an angle sensor is also provided to the cuff, and the angle formed by an air bag is detected. A straight line connecting the artery and the angle sensor when the angle sensor in the substantial center of the air bag is directly over the artery is used as a reference, and a determination is made based on a signal from the angle sensor during wearing of the cuff as to whether the angle of the straight line connecting the artery and the angle sensor from the abovementioned reference is less than a threshold value. This determination is made prior to blood pressure measurement and displayed. A user can therefore observe the display to achieve the proper fit of the cuff prior to measurement, and then perform a measurement.
In another disclosed blood pressure measurement device (see Patent Document 3, for example), by more accurately determining the positions of the cuff and the heart, blood pressure is measured without the measurement being affected by the subject's posture during measurement and fluctuation in physical characteristics of the subject. In this technique, the height of the cuff and heart is detected based on inputted values for the subject's upper arm length and forearm length, and detected angles for the pitch direction and roll direction of the forearm. Angle detection means for the upper arm is provided in addition to forearm angle detection means, and the height of the cuff and heart is detected based on the detected angles of the forearm and upper arm. Angles in the pitch direction and roll direction of the forearm are also detected by two-axis angle detection means, and the height of the cuff and heart is detected based on these detection values.
A blood pressure measurement device has also been disclosed (see Patent Document 4, for example) in which the body of the blood pressure measurement device worn by the subject is configured so as to be capable of integrally connecting with a processor, and the blood pressure measurement operation is automatically performed based on a mode inputted from the processor side.
In another disclosed blood pressure measurement device (see Patent Document 5, for example), a blood pressure measurement time or medication time is announced by a notification unit, and measurement can be reliably performed without being forgotten even when the device is used at home, and the measurement results are displayed by display means. Since the measurement results and measurement time are stored in a convenient memory for portability, a blood pressure trend diagram or other summary can be displayed by connecting an interface to a host computer during a hospital visit.